/*
 * Routines to compress and uncompess tcp packets (for transmission
 * over low speed serial lines.
 *
 * Copyright (c) 1989 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Berkeley.  The name of the
 * University may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
 *   Initial distribution.
 *
 * Modified June 1993 by Paul Mackerras, paulus@cs.anu.edu.au,
 * so that the entire packet being decompressed doesn't have
 * to be in contiguous memory (just the compressed header).
 *
 * Modified March 1998 by Guy Lancaster, glanca@gesn.com,
 * for a 16 bit processor.
 */

#include "netif/ppp/ppp_opts.h"
#if PPP_SUPPORT && VJ_SUPPORT /* don't build if not configured for use in lwipopts.h */

#include "netif/ppp/ppp_impl.h"
#include "netif/ppp/pppdebug.h"

#include "netif/ppp/vj.h"

#include <string.h>

#if LINK_STATS
#define INCR(counter) ++comp->stats.counter
#else
#define INCR(counter)
#endif

void vj_compress_init(struct vjcompress *comp)
{
    u8_t i;
    struct cstate *tstate = comp->tstate;

#if MAX_SLOTS == 0
    memset((char *)comp, 0, sizeof(*comp));
#endif
    comp->maxSlotIndex = MAX_SLOTS - 1;
    comp->compressSlot = 0; /* Disable slot ID compression by default. */

    for (i = MAX_SLOTS - 1; i > 0; --i) {
        tstate[i].cs_id = i;
        tstate[i].cs_next = &tstate[i - 1];
    }

    tstate[0].cs_next = &tstate[MAX_SLOTS - 1];
    tstate[0].cs_id = 0;
    comp->last_cs = &tstate[0];
    comp->last_recv = 255;
    comp->last_xmit = 255;
    comp->flags = VJF_TOSS;
}

/* ENCODE encodes a number that is known to be non-zero.  ENCODEZ
 * checks for zero (since zero has to be encoded in the long, 3 byte
 * form).
 */
#define ENCODE(n)                     \
    {                                 \
        if ((u16_t)(n) >= 256) {      \
            *cp++ = 0;                \
            cp[1] = (u8_t)(n);        \
            cp[0] = (u8_t)((n) >> 8); \
            cp += 2;                  \
        } else {                      \
            *cp++ = (u8_t)(n);        \
        }                             \
    }
#define ENCODEZ(n)                                  \
    {                                               \
        if ((u16_t)(n) >= 256 || (u16_t)(n) == 0) { \
            *cp++ = 0;                              \
            cp[1] = (u8_t)(n);                      \
            cp[0] = (u8_t)((n) >> 8);               \
            cp += 2;                                \
        } else {                                    \
            *cp++ = (u8_t)(n);                      \
        }                                           \
    }

#define DECODEL(f)                                               \
    {                                                            \
        if (*cp == 0) {                                          \
            u32_t tmp_ = lwip_ntohl(f) + ((cp[1] << 8) | cp[2]); \
            (f) = lwip_htonl(tmp_);                              \
            cp += 3;                                             \
        } else {                                                 \
            u32_t tmp_ = lwip_ntohl(f) + (u32_t)*cp++;           \
            (f) = lwip_htonl(tmp_);                              \
        }                                                        \
    }

#define DECODES(f)                                                      \
    {                                                                   \
        if (*cp == 0) {                                                 \
            u16_t tmp_ = lwip_ntohs(f) + (((u16_t)cp[1] << 8) | cp[2]); \
            (f) = lwip_htons(tmp_);                                     \
            cp += 3;                                                    \
        } else {                                                        \
            u16_t tmp_ = lwip_ntohs(f) + (u16_t)*cp++;                  \
            (f) = lwip_htons(tmp_);                                     \
        }                                                               \
    }

#define DECODEU(f)                                         \
    {                                                      \
        if (*cp == 0) {                                    \
            (f) = lwip_htons(((u16_t)cp[1] << 8) | cp[2]); \
            cp += 3;                                       \
        } else {                                           \
            (f) = lwip_htons((u16_t)*cp++);                \
        }                                                  \
    }

/* Helper structures for unaligned *u32_t and *u16_t accesses */
#ifdef PACK_STRUCT_USE_INCLUDES
#include "arch/bpstruct.h"
#endif
PACK_STRUCT_BEGIN
struct vj_u32_t {
    PACK_STRUCT_FIELD(u32_t v);
} PACK_STRUCT_STRUCT;
PACK_STRUCT_END
#ifdef PACK_STRUCT_USE_INCLUDES
#include "arch/epstruct.h"
#endif

#ifdef PACK_STRUCT_USE_INCLUDES
#include "arch/bpstruct.h"
#endif
PACK_STRUCT_BEGIN
struct vj_u16_t {
    PACK_STRUCT_FIELD(u16_t v);
} PACK_STRUCT_STRUCT;
PACK_STRUCT_END
#ifdef PACK_STRUCT_USE_INCLUDES
#include "arch/epstruct.h"
#endif

/*
 * vj_compress_tcp - Attempt to do Van Jacobson header compression on a
 * packet.  This assumes that nb and comp are not null and that the first
 * buffer of the chain contains a valid IP header.
 * Return the VJ type code indicating whether or not the packet was
 * compressed.
 */
u8_t vj_compress_tcp(struct vjcompress *comp, struct pbuf **pb)
{
    struct pbuf *np = *pb;
    struct ip_hdr *ip = (struct ip_hdr *)np->payload;
    struct cstate *cs = comp->last_cs->cs_next;
    u16_t ilen = IPH_HL(ip);
    u16_t hlen;
    struct tcp_hdr *oth;
    struct tcp_hdr *th;
    u16_t deltaS, deltaA = 0;
    u32_t deltaL;
    u32_t changes = 0;
    u8_t new_seq[16];
    u8_t *cp = new_seq;

    /*
     * Check that the packet is IP proto TCP.
     */
    if (IPH_PROTO(ip) != IP_PROTO_TCP) {
        return (TYPE_IP);
    }

    /*
     * Bail if this is an IP fragment or if the TCP packet isn't
     * `compressible' (i.e., ACK isn't set or some other control bit is
     * set).
     */
    if ((IPH_OFFSET(ip) & PP_HTONS(0x3fff)) || np->tot_len < 40) {
        return (TYPE_IP);
    }

    th = (struct tcp_hdr *)&((struct vj_u32_t *)ip)[ilen];

    if ((TCPH_FLAGS(th) & (TCP_SYN | TCP_FIN | TCP_RST | TCP_ACK)) != TCP_ACK) {
        return (TYPE_IP);
    }

    /* Check that the TCP/IP headers are contained in the first buffer. */
    hlen = ilen + TCPH_HDRLEN(th);
    hlen <<= 2;

    if (np->len < hlen) {
        PPPDEBUG(LOG_INFO, ("vj_compress_tcp: header len %d spans buffers\n", hlen));
        return (TYPE_IP);
    }

    /* TCP stack requires that we don't change the packet payload, therefore we copy
     * the whole packet before compression. */
    np = pbuf_clone(PBUF_RAW, PBUF_RAM, *pb);

    if (!np) {
        return (TYPE_IP);
    }

    *pb = np;
    ip = (struct ip_hdr *)np->payload;

    /*
     * Packet is compressible -- we're going to send either a
     * COMPRESSED_TCP or UNCOMPRESSED_TCP packet.  Either way we need
     * to locate (or create) the connection state.  Special case the
     * most recently used connection since it's most likely to be used
     * again & we don't have to do any reordering if it's used.
     */
    INCR(vjs_packets);

    if (!ip4_addr_cmp(&ip->src, &cs->cs_ip.src) || !ip4_addr_cmp(&ip->dest, &cs->cs_ip.dest) || (*(struct vj_u32_t *)th).v != (((struct vj_u32_t *)&cs->cs_ip)[IPH_HL(&cs->cs_ip)]).v) {
        /*
         * Wasn't the first -- search for it.
         *
         * States are kept in a circularly linked list with
         * last_cs pointing to the end of the list.  The
         * list is kept in lru order by moving a state to the
         * head of the list whenever it is referenced.  Since
         * the list is short and, empirically, the connection
         * we want is almost always near the front, we locate
         * states via linear search.  If we don't find a state
         * for the datagram, the oldest state is (re-)used.
         */
        struct cstate *lcs;
        struct cstate *lastcs = comp->last_cs;

        do {
            lcs = cs;
            cs = cs->cs_next;
            INCR(vjs_searches);

            if (ip4_addr_cmp(&ip->src, &cs->cs_ip.src) && ip4_addr_cmp(&ip->dest, &cs->cs_ip.dest) && (*(struct vj_u32_t *)th).v == (((struct vj_u32_t *)&cs->cs_ip)[IPH_HL(&cs->cs_ip)]).v) {
                goto found;
            }
        } while (cs != lastcs);

        /*
         * Didn't find it -- re-use oldest cstate.  Send an
         * uncompressed packet that tells the other side what
         * connection number we're using for this conversation.
         * Note that since the state list is circular, the oldest
         * state points to the newest and we only need to set
         * last_cs to update the lru linkage.
         */
        INCR(vjs_misses);
        comp->last_cs = lcs;
        goto uncompressed;

    found:

        /*
         * Found it -- move to the front on the connection list.
         */
        if (cs == lastcs) {
            comp->last_cs = lcs;
        } else {
            lcs->cs_next = cs->cs_next;
            cs->cs_next = lastcs->cs_next;
            lastcs->cs_next = cs;
        }
    }

    oth = (struct tcp_hdr *)&((struct vj_u32_t *)&cs->cs_ip)[ilen];
    deltaS = ilen;

    /*
     * Make sure that only what we expect to change changed. The first
     * line of the `if' checks the IP protocol version, header length &
     * type of service.  The 2nd line checks the "Don't fragment" bit.
     * The 3rd line checks the time-to-live and protocol (the protocol
     * check is unnecessary but costless).  The 4th line checks the TCP
     * header length.  The 5th line checks IP options, if any.  The 6th
     * line checks TCP options, if any.  If any of these things are
     * different between the previous & current datagram, we send the
     * current datagram `uncompressed'.
     */
    if ((((struct vj_u16_t *)ip)[0]).v != (((struct vj_u16_t *)&cs->cs_ip)[0]).v || (((struct vj_u16_t *)ip)[3]).v != (((struct vj_u16_t *)&cs->cs_ip)[3]).v || (((struct vj_u16_t *)ip)[4]).v != (((struct vj_u16_t *)&cs->cs_ip)[4]).v || TCPH_HDRLEN(th) != TCPH_HDRLEN(oth) || (deltaS > 5 && BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || (TCPH_HDRLEN(th) > 5 && BCMP(th + 1, oth + 1, (TCPH_HDRLEN(th) - 5) << 2))) {
        goto uncompressed;
    }

    /*
     * Figure out which of the changing fields changed.  The
     * receiver expects changes in the order: urgent, window,
     * ack, seq (the order minimizes the number of temporaries
     * needed in this section of code).
     */
    if (TCPH_FLAGS(th) & TCP_URG) {
        deltaS = lwip_ntohs(th->urgp);
        ENCODEZ(deltaS);
        changes |= NEW_U;
    } else if (th->urgp != oth->urgp) {
        /* argh! URG not set but urp changed -- a sensible
         * implementation should never do this but RFC793
         * doesn't prohibit the change so we have to deal
         * with it. */
        goto uncompressed;
    }

    if ((deltaS = (u16_t)(lwip_ntohs(th->wnd) - lwip_ntohs(oth->wnd))) != 0) {
        ENCODE(deltaS);
        changes |= NEW_W;
    }

    if ((deltaL = lwip_ntohl(th->ackno) - lwip_ntohl(oth->ackno)) != 0) {
        if (deltaL > 0xffff) {
            goto uncompressed;
        }

        deltaA = (u16_t)deltaL;
        ENCODE(deltaA);
        changes |= NEW_A;
    }

    if ((deltaL = lwip_ntohl(th->seqno) - lwip_ntohl(oth->seqno)) != 0) {
        if (deltaL > 0xffff) {
            goto uncompressed;
        }

        deltaS = (u16_t)deltaL;
        ENCODE(deltaS);
        changes |= NEW_S;
    }

    switch (changes) {
        case 0:

            /*
             * Nothing changed. If this packet contains data and the
             * last one didn't, this is probably a data packet following
             * an ack (normal on an interactive connection) and we send
             * it compressed.  Otherwise it's probably a retransmit,
             * retransmitted ack or window probe.  Send it uncompressed
             * in case the other side missed the compressed version.
             */
            if (IPH_LEN(ip) != IPH_LEN(&cs->cs_ip) &&
                lwip_ntohs(IPH_LEN(&cs->cs_ip)) == hlen) {
                break;
            }

            /* no break */
            /* fall through */

        case SPECIAL_I:
        case SPECIAL_D:
            /*
             * actual changes match one of our special case encodings --
             * send packet uncompressed.
             */
            goto uncompressed;

        case NEW_S | NEW_A:
            if (deltaS == deltaA && deltaS == lwip_ntohs(IPH_LEN(&cs->cs_ip)) - hlen) {
                /* special case for echoed terminal traffic */
                changes = SPECIAL_I;
                cp = new_seq;
            }

            break;

        case NEW_S:
            if (deltaS == lwip_ntohs(IPH_LEN(&cs->cs_ip)) - hlen) {
                /* special case for data xfer */
                changes = SPECIAL_D;
                cp = new_seq;
            }

            break;

        default:
            break;
    }

    deltaS = (u16_t)(lwip_ntohs(IPH_ID(ip)) - lwip_ntohs(IPH_ID(&cs->cs_ip)));

    if (deltaS != 1) {
        ENCODEZ(deltaS);
        changes |= NEW_I;
    }

    if (TCPH_FLAGS(th) & TCP_PSH) {
        changes |= TCP_PUSH_BIT;
    }

    /*
     * Grab the cksum before we overwrite it below.  Then update our
     * state with this packet's header.
     */
    deltaA = lwip_ntohs(th->chksum);
    MEMCPY(&cs->cs_ip, ip, hlen);

    /*
     * We want to use the original packet as our compressed packet.
     * (cp - new_seq) is the number of bytes we need for compressed
     * sequence numbers.  In addition we need one byte for the change
     * mask, one for the connection id and two for the tcp checksum.
     * So, (cp - new_seq) + 4 bytes of header are needed.  hlen is how
     * many bytes of the original packet to toss so subtract the two to
     * get the new packet size.
     */
    deltaS = (u16_t)(cp - new_seq);

    if (!comp->compressSlot || comp->last_xmit != cs->cs_id) {
        comp->last_xmit = cs->cs_id;
        hlen -= deltaS + 4;

        if (pbuf_remove_header(np, hlen)) {
            /* Can we cope with this failing?  Just assert for now */
            LWIP_ASSERT("pbuf_remove_header failed\n", 0);
        }

        cp = (u8_t *)np->payload;
        *cp++ = (u8_t)(changes | NEW_C);
        *cp++ = cs->cs_id;
    } else {
        hlen -= deltaS + 3;

        if (pbuf_remove_header(np, hlen)) {
            /* Can we cope with this failing?  Just assert for now */
            LWIP_ASSERT("pbuf_remove_header failed\n", 0);
        }

        cp = (u8_t *)np->payload;
        *cp++ = (u8_t)changes;
    }

    *cp++ = (u8_t)(deltaA >> 8);
    *cp++ = (u8_t)deltaA;
    MEMCPY(cp, new_seq, deltaS);
    INCR(vjs_compressed);
    return (TYPE_COMPRESSED_TCP);

    /*
     * Update connection state cs & send uncompressed packet (that is,
     * a regular ip/tcp packet but with the 'conversation id' we hope
     * to use on future compressed packets in the protocol field).
     */
uncompressed:
    MEMCPY(&cs->cs_ip, ip, hlen);
    IPH_PROTO_SET(ip, cs->cs_id);
    comp->last_xmit = cs->cs_id;
    return (TYPE_UNCOMPRESSED_TCP);
}

/*
 * Called when we may have missed a packet.
 */
void vj_uncompress_err(struct vjcompress *comp)
{
    comp->flags |= VJF_TOSS;
    INCR(vjs_errorin);
}

/*
 * "Uncompress" a packet of type TYPE_UNCOMPRESSED_TCP.
 * Return 0 on success, -1 on failure.
 */
int vj_uncompress_uncomp(struct pbuf *nb, struct vjcompress *comp)
{
    u32_t hlen;
    struct cstate *cs;
    struct ip_hdr *ip;

    ip = (struct ip_hdr *)nb->payload;
    hlen = IPH_HL(ip) << 2;

    if (IPH_PROTO(ip) >= MAX_SLOTS || hlen + sizeof(struct tcp_hdr) > nb->len || (hlen += TCPH_HDRLEN_BYTES((struct tcp_hdr *)&((char *)ip)[hlen])) > nb->len || hlen > MAX_HDR) {
        PPPDEBUG(LOG_INFO, ("vj_uncompress_uncomp: bad cid=%d, hlen=%d buflen=%d\n",
                            IPH_PROTO(ip), hlen, nb->len));
        vj_uncompress_err(comp);
        return -1;
    }

    cs = &comp->rstate[comp->last_recv = IPH_PROTO(ip)];
    comp->flags &= ~VJF_TOSS;
    IPH_PROTO_SET(ip, IP_PROTO_TCP);
    /* copy from/to bigger buffers checked above instead of cs->cs_ip and ip
       just to help static code analysis to see this is correct ;-) */
    MEMCPY(&cs->cs_hdr, nb->payload, hlen);
    cs->cs_hlen = (u16_t)hlen;
    INCR(vjs_uncompressedin);
    return 0;
}

/*
 * Uncompress a packet of type TYPE_COMPRESSED_TCP.
 * The packet is composed of a buffer chain and the first buffer
 * must contain an accurate chain length.
 * The first buffer must include the entire compressed TCP/IP header.
 * This procedure replaces the compressed header with the uncompressed
 * header and returns the length of the VJ header.
 */
int vj_uncompress_tcp(struct pbuf **nb, struct vjcompress *comp)
{
    u8_t *cp;
    struct tcp_hdr *th;
    struct cstate *cs;
    struct vj_u16_t *bp;
    struct pbuf *n0 = *nb;
    u32_t tmp;
    u32_t vjlen, hlen, changes;

    INCR(vjs_compressedin);
    cp = (u8_t *)n0->payload;
    changes = *cp++;

    if (changes & NEW_C) {
        /*
         * Make sure the state index is in range, then grab the state.
         * If we have a good state index, clear the 'discard' flag.
         */
        if (*cp >= MAX_SLOTS) {
            PPPDEBUG(LOG_INFO, ("vj_uncompress_tcp: bad cid=%d\n", *cp));
            goto bad;
        }

        comp->flags &= ~VJF_TOSS;
        comp->last_recv = *cp++;
    } else {
        /*
         * this packet has an implicit state index.  If we've
         * had a line error since the last time we got an
         * explicit state index, we have to toss the packet.
         */
        if (comp->flags & VJF_TOSS) {
            PPPDEBUG(LOG_INFO, ("vj_uncompress_tcp: tossing\n"));
            INCR(vjs_tossed);
            return (-1);
        }
    }

    cs = &comp->rstate[comp->last_recv];
    hlen = IPH_HL(&cs->cs_ip) << 2;
    th = (struct tcp_hdr *)&((u8_t *)&cs->cs_ip)[hlen];
    th->chksum = lwip_htons((*cp << 8) | cp[1]);
    cp += 2;

    if (changes & TCP_PUSH_BIT) {
        TCPH_SET_FLAG(th, TCP_PSH);
    } else {
        TCPH_UNSET_FLAG(th, TCP_PSH);
    }

    switch (changes & SPECIALS_MASK) {
        case SPECIAL_I: {
            u32_t i = lwip_ntohs(IPH_LEN(&cs->cs_ip)) - cs->cs_hlen;
            /* some compilers can't nest inline assembler.. */
            tmp = lwip_ntohl(th->ackno) + i;
            th->ackno = lwip_htonl(tmp);
            tmp = lwip_ntohl(th->seqno) + i;
            th->seqno = lwip_htonl(tmp);
        } break;

        case SPECIAL_D:
            /* some compilers can't nest inline assembler.. */
            tmp = lwip_ntohl(th->seqno) + lwip_ntohs(IPH_LEN(&cs->cs_ip)) - cs->cs_hlen;
            th->seqno = lwip_htonl(tmp);
            break;

        default:
            if (changes & NEW_U) {
                TCPH_SET_FLAG(th, TCP_URG);
                DECODEU(th->urgp);
            } else {
                TCPH_UNSET_FLAG(th, TCP_URG);
            }

            if (changes & NEW_W) {
                DECODES(th->wnd);
            }

            if (changes & NEW_A) {
                DECODEL(th->ackno);
            }

            if (changes & NEW_S) {
                DECODEL(th->seqno);
            }

            break;
    }

    if (changes & NEW_I) {
        DECODES(cs->cs_ip._id);
    } else {
        IPH_ID_SET(&cs->cs_ip, lwip_ntohs(IPH_ID(&cs->cs_ip)) + 1);
        IPH_ID_SET(&cs->cs_ip, lwip_htons(IPH_ID(&cs->cs_ip)));
    }

    /*
     * At this point, cp points to the first byte of data in the
     * packet.  Fill in the IP total length and update the IP
     * header checksum.
     */
    vjlen = (u16_t)(cp - (u8_t *)n0->payload);

    if (n0->len < vjlen) {
        /*
         * We must have dropped some characters (crc should detect
         * this but the old slip framing won't)
         */
        PPPDEBUG(LOG_INFO, ("vj_uncompress_tcp: head buffer %d too short %d\n",
                            n0->len, vjlen));
        goto bad;
    }

#if BYTE_ORDER == LITTLE_ENDIAN
    tmp = n0->tot_len - vjlen + cs->cs_hlen;
    IPH_LEN_SET(&cs->cs_ip, lwip_htons((u16_t)tmp));
#else
    IPH_LEN_SET(&cs->cs_ip, lwip_htons(n0->tot_len - vjlen + cs->cs_hlen));
#endif

    /* recompute the ip header checksum */
    bp = (struct vj_u16_t *)&cs->cs_ip;
    IPH_CHKSUM_SET(&cs->cs_ip, 0);

    for (tmp = 0; hlen > 0; hlen -= 2) {
        tmp += (*bp++).v;
    }

    tmp = (tmp & 0xffff) + (tmp >> 16);
    tmp = (tmp & 0xffff) + (tmp >> 16);
    IPH_CHKSUM_SET(&cs->cs_ip, (u16_t)(~tmp));

    /* Remove the compressed header and prepend the uncompressed header. */
    if (pbuf_remove_header(n0, vjlen)) {
        /* Can we cope with this failing?  Just assert for now */
        LWIP_ASSERT("pbuf_remove_header failed\n", 0);
        goto bad;
    }

    if (LWIP_MEM_ALIGN(n0->payload) != n0->payload) {
        struct pbuf *np;

#if IP_FORWARD
        /* If IP forwarding is enabled we are using a PBUF_LINK packet type so
         * the packet is being allocated with enough header space to be
         * forwarded (to Ethernet for example).
         */
        np = pbuf_alloc(PBUF_LINK, n0->len + cs->cs_hlen, PBUF_POOL);
#else /* IP_FORWARD */
        np = pbuf_alloc(PBUF_RAW, n0->len + cs->cs_hlen, PBUF_POOL);
#endif /* IP_FORWARD */

        if (!np) {
            PPPDEBUG(LOG_WARNING, ("vj_uncompress_tcp: realign failed\n"));
            goto bad;
        }

        if (pbuf_remove_header(np, cs->cs_hlen)) {
            /* Can we cope with this failing?  Just assert for now */
            LWIP_ASSERT("pbuf_remove_header failed\n", 0);
            goto bad;
        }

        pbuf_take(np, n0->payload, n0->len);

        if (n0->next) {
            pbuf_chain(np, n0->next);
            pbuf_dechain(n0);
        }

        pbuf_free(n0);
        n0 = np;
    }

    if (pbuf_add_header(n0, cs->cs_hlen)) {
        struct pbuf *np;

        LWIP_ASSERT("vj_uncompress_tcp: cs->cs_hlen <= PBUF_POOL_BUFSIZE", cs->cs_hlen <= PBUF_POOL_BUFSIZE);
        np = pbuf_alloc(PBUF_RAW, cs->cs_hlen, PBUF_POOL);

        if (!np) {
            PPPDEBUG(LOG_WARNING, ("vj_uncompress_tcp: prepend failed\n"));
            goto bad;
        }

        pbuf_cat(np, n0);
        n0 = np;
    }

    LWIP_ASSERT("n0->len >= cs->cs_hlen", n0->len >= cs->cs_hlen);
    MEMCPY(n0->payload, &cs->cs_ip, cs->cs_hlen);

    *nb = n0;

    return vjlen;

bad:
    vj_uncompress_err(comp);
    return (-1);
}

#endif /* PPP_SUPPORT && VJ_SUPPORT */
